1. Technical Field
The present invention relates to a liquid sensing device to sense the level of remaining liquid (ink) particularly in a liquid consuming system such as an inkjet recording device and a liquid container provided to such a device.
2. Description of the Related Art
One representative example of a conventional liquid consuming device is an inkjet recording device equipped with an inkjet recording head for printing images. Examples of other liquid jetting devices are devices equipped with a coloring matter jetting head used to manufacture color filters in liquid crystal displays; devices equipped with an electrode material (electrode paste) jetting head used to produce electrodes in organic EL displays, field emission displays (FED) or the like; devices equipped with a bioorganic substance jetting head used in biochip manufacture; and devices equipped with a specimen jetting head as a precision pipette.
In an inkjet recording device, a typical example of such a liquid consuming device, an inkjet recording head that is furnished with pressure generating means adapted to pressurize a pressure generating chamber and with nozzle apertures for ejecting the pressurized ink as ink drops is installed on a carriage. The design makes possible intermittent printing by continuing to supply ink inside an ink storage receptacle to the recording head via a flow channel. The ink storage receptacle is designed as a detachable cartridge, enabling the user to easily replace it when the ink has been consumed, for example.
Past methods for monitoring ink consumption in an ink cartridge include methods involving monitoring through calculation of ink consumption by software adapted to cumulate the number of ink drops ejected by the head or the amount of ink suctioned by maintenance operations; or methods involving monitoring of the point in time that a prescribed amount of ink has actually been consumed, by installing electrodes for sensing the liquid level in the ink cartridge.
However, methods involving monitoring through software calculation of ink consumption based on cumulative number of ink drops ejected by the head or amount of ink has drawbacks such as the following. There is some variability among heads in the weight of ejected ink drops. While such variability in weight of ejected ink drops has no discernible effect on print quality, in consideration of cumulative errors in ink consumption due to such variations, ink cartridges are typically filled with ink in amounts that provide a margin for this. A consequent problem is that, depending on the individual cartridge, there will be an excess of ink in an amount equivalent to this margin.
On the other hand, methods involving monitoring the point in time that the ink has been consumed with electrodes affords highly reliable monitoring of remaining ink level, since actual ink level can be detected. However, drawbacks are that since the ability to detect the ink level depends on the conductivity of the ink, the types of ink that can be detected is limited; and that a complicated sealing structure will be needed for the electrodes. Additionally, because the materials for the electrodes are typically noble metals (which have good conductivity and high corrosion resistance), ink cartridge production costs will be higher. Also, because two electrodes must be installed, there are more manufacturing steps, and production costs will be higher as a result.
In Patent Citation 1, a piezoelectric device (herein termed a “sensor unit”) is disclosed as a device adapted to overcome the above problems. This sensor unit monitors the amount of remaining ink in the ink cartridge, by utilizing the fact that the resonance frequency of a residual vibration signal produced by residual vibration (free vibration) of an oscillator plate subsequent to forced oscillation will vary depending on whether or not ink is present in a cavity facing the oscillator plate on which the piezoelectric element has been stacked.
In Patent Citation 2 there is disclosed a liquid sensing device equipped with a sensor chip that has a sensor cavity (232) for receiving the liquid targeted for sensing and that includes a piezoelectric element for imparting oscillation at least to this sensor cavity (232); a sensor base (220) that is joined to the sensor cavity (232) side; a first hole (222) provided in the sensor base (220) and adapted to conduct the liquid into the sensor cavity (232); a second hole (223) provided in the sensor base (220) and adapted to drain liquid from the sensor cavity (232); a downstream buffer chamber (123) for retaining liquid drained from the second hole (223); and an outlet (125) for the liquid from the downstream buffer chamber (123).
[Patent Citation 1] Japanese Unexamined Patent Publication 2001 13′16030 2001-146030
[Patent Citation 2] Japanese Unexamined Patent Publication 2006-281550
The basic principle of sensing disclosed in Patent Citation 1 can be fulfilled with the technology of Patent Citation 2; and where there is a sufficient amount of liquid in sensing target (e.g. a liquid container), specifically, where the sensor cavity (232), the first hole (222), the second hole (223), and the downstream buffer chamber (123) that together constitute the fluid flow channel are filled with liquid, it will be possible to accurately sense that “sufficient liquid is present.”
However, with the technology of Patent Citation 2, in the event that for example there is only a small amount of remaining liquid in the liquid container, in some instances it may not be possible to accurately detect this fact (i.e. the fact that the remaining liquid level is less than a prescribed level). Where the remaining liquid level has dropped to less than a prescribed level, under normal circumstances air will enter (and liquid will disappear from) the sensor cavity (232), the first hole (222), the second hole (223), and the downstream buffer chamber (123) that constitute the fluid flow channel, and the sensor chip should be able to detect this fact.
However, in the prior art, in some instances a considerable of liquid will remain in the buffer chamber despite the remaining liquid level in the liquid container having dropped to less than the prescribed level, for example. Since the buffer chamber has a large liquid storage capacity, the extent of remaining liquid in the buffer chamber will have an appreciable effect on whether or not liquid is sensed. If a large amount of liquid is present in the buffer chamber, the sensor chip will sense that “sufficient liquid is still present” in the liquid container. On the other hand, if there is too little liquid in the liquid container, and as a result the liquid in the buffer chamber is less than the prescribed level, the sensor chip will sense that “the remaining liquid level is less than the prescribed level” in the liquid container.
Since in the prior art one encounters instances in which a considerable of liquid will remain in the buffer chamber despite the remaining liquid level in the liquid container having dropped to less than the prescribed level for example, in such instances it may be sensed in error that “sufficient liquid is still present” in the liquid container.